1. Field of the Invention
The present invention relates to a method and to a system for calculating pressure drops in a circuit by taking account of the thermal effects along the circuit.
2. Description of the Prior Art
U.S. Pat. No. 5,850,621 describes a computer method allowing calculation of pressure drops in parts of a circuit such as a well drilled in the ground, the inner space of drillpipes or of tubes in the well, the annular space between these pipes or tubes and the well wall. Known pressure drop calculation methods account for the data relative to the well pattern, the characteristics of the circulating fluid and the flow conditions. In most calculation models, a rheology that is representative of the fluid is taken into account: Bingham, Ostwald or other models. Some models also account for the influence of the rotation of the pipes and/or of the eccentricity in the well. However, these calculation models do not account for the influence of the temperature variation and/or of the pressure variation on is the rheology of the fluid, a relatively important parameter for pressure drop calculation. Now, the temperature and pressure conditions in a wellbore, offshore or onshore, are excessively variable, which currently leads to miscalculations.
The present invention relates to a method of calculating pressure drops created by a fluid in a circuit having a determined thermal profile. The following steps are carried out:
making up a database giving the rheology of various fluids at least according to the temperature;
segmenting the thermal profile into sections and determining a temperature value representative of that of the fluid in the sections;
using the database for determining the rheology of the fluid in each section at the representative temperature; and
calculating and adding up the pressure drops in each section considering the determined rheology.
The thermal profile can be segmented for a substantially constant temperature range.
The mean temperature of the fluid in each section can be taken as the representative temperature.
The database can comprise the rheology of fluids according to the pressure.
The mean pressure of the fluid in each section can be taken into account for determining the rheology of the fluid in said section.
The database can be organized in fluid families.
The database can comprise laws relative to the rheology variation according to the temperature and/or the pressure for each fluid family.
The invention also relates to a system for calculating pressure drops in a circuit by implementing the method described above, the system comprising means for segmenting the thermal profile along the circuit; means for managing a database giving the rheology of various fluids according to the temperature and/or the pressure; and means for calculating pressure drops in each section.
The method is advantageously applied to calculation of pressure drops in a well in the process of being drilled.
The present method is implemented for accounting for the influence, notably, of thermal effects on the pressure drop through the rheology of the fluid. The evolution of the temperature and of the pressure in the well locally modifies the viscosity of the mud and therefore the generated pressure drops. The precision of interpretation of the value and of the variations of the discharge pressure measured at the surface is greatly improved.